The present invention relates generally to improvements in portable, combustion-powered fastener driving tools, and more particularly to a mount for a combustion chamber fan motor.
Portable, combustion-powered fastener driving tools are used for driving fasteners into workpieces. Exemplary embodiments of fastener driving tools are described in U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439; and Re. 32,452, all of which are incorporated by reference herein. Particular embodiments of fastener driving tools are sold, for example, by Illinois Tool Works of Vernon Hills, Ill., under the IMPULSE® and TRIMMASTER® brands.
Tools of the type noted above typically incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides an efficient combustion within the chamber and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or “ready” position through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. This combined downward movement causes a reactive force or recoil of the tool body. Hence, the fan motor, which is suspended in the tool body, is subjected to acceleration in a direction opposite the power stroke of the piston/driver blade and fastener.
Then, within milliseconds, the momentum of the piston/driver blade assembly is stopped by the bumper at the opposite end of the cylinder, and the tool body is accelerated toward the workpiece. Therefore, the fan motor and shaft are subjected to an acceleration force that is opposite the direction of the first acceleration. These reciprocal accelerations cause the fan motor to oscillate with respect to the tool. The magnitude of these accelerations, if left unmanaged, is detrimental to the life and reliability of the combustion chamber fan motor.
Recent portable, combustion-powered fastener driving tools address the problems of motor acceleration and oscillation by including a suspension mechanism that suspends the fan motor within a cavity of the cylinder head. The suspension mechanism reduces the effects of the reciprocal axial accelerations and the resulting oscillation of the motor during operation of the tool, and allows the use of a standard, iron-core motor in the tool. Before such suspension mechanisms, specially designed motors were required in the tools to withstand the reciprocal accelerations, resulting in increased production costs.
Exemplary embodiments of such recent suspension mechanisms are described in commonly assigned EP 1 197 300 and EP 0 925 880, the entireties of which are incorporated herein by reference. The type of suspension mechanism described in EP '300 and EP '880 suspends the motor, for example, within a depending cavity in the center of a cylinder head. The suspension mechanisms include a flexible rubber web, which may be vulcanized or bonded to a retaining mechanism securing the fan motor, such as a retaining ring or cup. The web is also vulcanized or bonded to a mechanism such as a steel mounting bracket or steel ring, radially spaced from the retaining ring and secured to the cylinder head. Only the resilient web secures the retaining mechanism holding the motor to the cylinder head. The rubber web may be provided with a number of preferably blind end bores.
These and similar types of suspension mechanisms reduce or dampen operationally-induced reciprocal accelerations of the motor while keeping the oscillations of the motor within an acceptable range, thus extending the life of the motor. Because a standard motor can be used in a portable tool having the suspension mechanisms, production costs of the tool can be reduced.
However, it has been difficult and costly to produce the present suspension mechanism, due to, among other things, the costs of stamping the rubber web and vulcanizing or bonding the rubber web. Due to continuing commercial pressure on manufacturers to lower prices, there is a need to provide a combustion chamber fan motor suspension which substantially provides the benefits of prior art suspensions at a reduced manufacturing cost.